During the fabrication of semiconductor devices, micro-features on the surface of the substrate are sometimes created in order to isolate devices or to create other devices such as capacitors etc. These micro-features are later filled, often by using silane (SiH4). As circuit geometries shrink to ever smaller feature sizes, the aspect ratios (ratio of depth to width) of micro-features on substrates increase, see FIG. 1. When using a silane only, poly-silicon fill process, the level of defects inside the micro-feature increases as the micro-feature aspect ratio increases. Additionally, as absolute dimensions decrease, new mechanisms of defect generation not dependent on the micro-feature aspect ratio arise. One common defect is the creation of voids inside the micro-feature. These voids cause areas of high electrical resistance and may interfere with circuit operation.
Several possible causes of void formation are: depletion of deposition gas, differing nucleation characteristics, the presence of gas phase radicals, and hydrogen outgassing from the deposited film.